Question

I have a program that has two separate sections: one of them should be executed when the network interface is wireless LAN and the other one when it’s a wired LAN connection. How can I know that inside of my program? What function should I use to get that information?

Answer 1

You can use the iwconfig command from the command line:

$ iwconfig
lo        no wireless extensions.
eth0      no wireless extensions.

If you need to use it from C, as @opaque’s link above explains, get the sources or use strace to see which ioctls() you need to use:

ioctl(3, SIOCGIWNAME, 0x7fff82c0d040)   = -1 EOPNOTSUPP (Operation not supported)
ioctl(3, SIOCGIFFLAGS, {ifr_name="lo", ifr_flags=IFF_UP|IFF_LOOPBACK|IFF_RUNNING}) = 0
write(2, "lo        no wireless extensions"..., 35lo        no wireless extensions.

) = 35
ioctl(3, SIOCGIWNAME, 0x7fff82c0d040)   = -1 EOPNOTSUPP (Operation not supported)
ioctl(3, SIOCGIFFLAGS, {ifr_name="eth0", ifr_flags=IFF_UP|IFF_BROADCAST|IFF_RUNNING|IFF_MULTICAST}) = 0
write(2, "eth0      no wireless extensions"..., 35eth0      no wireless extensions.

) = 35

See SIOCGIWNAME usage:

#define SIOCGIWNAME 0x8B01 /* get name == wireless protocol */
/* SIOCGIWNAME is used to verify the presence of Wireless Extensions.
* Common values : "IEEE 802.11-DS", "IEEE 802.11-FH", "IEEE 802.11b"...